Rogue Enzymes at Work–Unraveling the Interplay Between Lipase and Lipoxygenase in Pearl Millet Flour for Solving the Problem of Rancidity

Pearl millet, a nutritionally superior and climate-resilient cereal, faces a major bottleneck in its post-milling shelf life due to rapid flour rancidity. This spoilage is primarily enzymatic, driven by the sequential action of two key enzymes-triacylglycerol lipase (TAG-lipase) and lipoxygenase (LOX). Lipase, a serine hydrolase of the α/β-hydrolase fold family, initiates hydrolytic rancidity by cleaving triacylglycerols (TAGs) into free fatty acids (FFAs). These liberated FFAs (linoleic and oleic acids) become substrates for LOX, which oxidizes them into hydroperoxides, aldehydes, and volatile compounds (hexanal, 2,4-decadienal), producing off-flavors in the flour. While both enzymes contribute to flour spoilage, lipase acts as the biochemical gatekeeper, generating the FFA pool that enables LOX activity. This review dissects the distinct structural features, catalytic mechanisms, and substrate preferences of lipase and LOX, highlighting their roles in rancidity onset and progression. Recent transcriptomic analyses have identified allelic variants of PgTAGLip1/Lip2 associated with reduced lipase activity and improved flour stability. In contrast, LOX activity appears secondary and more responsive to oxidative conditions. Processing interventions such as microwave heating, antioxidant incorporation, and defatting offer short- to medium-term solutions. However, long-term strategies lie in targeted genome editing-particularly CRISPR/Cas9-based inactivation of lipase and LOX isoforms. Integrating enzymatic, genetic, and processing-based approaches provides a comprehensive framework to enhance the shelf life and commercial viability of pearl millet flour. There is an urgent need to prioritize lipase suppression and offer a roadmap for developing low rancid pearl millet cultivars to unlock the full nutritional and economic potential of pearl millet.